Gas turbine engines for power plants are being developed with larger gas flow areas for improved efficiencies, thereby requiring larger turbine blades than in previous designs. A high working gas temperature also increases efficiency. When a large blade size is combined with high rotational speed and high temperature, the resultant loading on a blade and its attachment slot in the turbine rotor disk can be very high. Centrifugal force increases with blade mass and length. These factors also increase potential vibration problems. A part-span snubber or tip shroud can reduce vibration, but these devices become problematic with increased blade size.
Blade mass and temperature have been reduced in smaller cast blades by incorporating cored passages for cooling and weight reduction. Such blades have load-bearing airfoil walls, in which the cumulative centrifugal loading of the blade is carried radially inward toward the blade root via the outermost wall. The terms “radial” or “radially” as used herein means relative to the rotation axis of the turbine rotor or disk, generally along a line connecting the tip and the base of the airfoil. The wall thickness at the blade tip affects the thickness required at the root to carry the resultant load from the rotating mass. The minimum practical wall thickness is determined by casting tolerances, and the resulting centrifugal loadings are a limiting factor in designing very large blades for new engine designs.